STEEL AND TIMBER (Module 1)

What are the two primary ultimate load design approaches used in structural steel design?

Load and Resistance Factor Design (LRFD) and Allowable Strength Design (ASD) [or Allowable Stress Design].

The stress at which a material exhibits a specified permanent deformation or begins to deform plastically without an increase in load.

Yield Strength (Fy)

The maximum stress that a material can withstand while being stretched or pulled before necking or breaking occurs.

Tensile Strength (Fu)

is the process of determining the “response” of a structure due to external “actions”

Structural Analysis

the structure includes changes in the geometry (displacements or deformations) and/or changes in the state of stress of the structure

Response

the anticipated forces or loads during the lifetime of the structure

Actions

the selection of the arrangement and sizes of structural elements so that the service loads may be safely carried, and displacements are within acceptable limits

Structural framework design

ensures that intended results are achieved, such as:

a. Adequate working areas and clearances
b. Proper ventilation and/or air-conditioning
c. Adequate mobility or transportation facilities such as elevators, stairways, and cranes, etc.
d. Adequate lighting, and e. Aesthetics

Functional design

STRUCTURAL DESIGN PROCEDURE

establish functions of the structure and set criteria for arriving at an optimum design.

Planning

STRUCTURAL DESIGN PROCEDURE

arrangement of the elements to serve the function in 1.

Preliminary structural configuration

STRUCTURAL DESIGN PROCEDURE

select member sizes to satisfy an objective criterion, such as least weight or cost.

Preliminary member selection

STRUCTURAL DESIGN PROCEDURE

structural analysis involving modeling the loads and structural framework to obtain internal forces and any desired deflections.

Analysis

STRUCTURAL DESIGN PROCEDURE

structural member sizes are determined to satisfy the requirements of the structural analysis.

Design

STRUCTURAL DESIGN PROCEDURE

are all strength and serviceability requirements satisfied and is the result optimal? Compare with predetermined criteria.

Evaluation

BASIC DESIGN PRINCIPLE

Capacity ≥ Demand

Resistance ≥ Load

R ≥ Q

are static forces that are relatively constant for an extended time.

Dead Load

the dead weight of a structure includes its full weight.

Self-weight
:floors, walls, slabs, ceilings, columns, beams, staircases

permanent appliances and any fixed decoration

Superimposed Dead Loads (SDL)

are usually variable or moving loads and are usually referred to occupational forces from occupancy and intended use.

Live Load

STRUCTURAL LOADINGS

3. Wind Load
4. Earthquake Load
5. Snow Loads
6. Hydrostatic Loads
7. Special Loads

It is a condition of a structure at which it ceases to fulfill its intended function.

LIMIT STATES

maximum ductile strength, buckling, fatigue, fracture, overturning, and sliding.

Strength Limit State

deflection, vibration, permanent deformation, cracking

Serviceability Limit State

is that unit tensile stress at which the stress-strain curve exhibits a well-defined increase in deformation without an increase in stress.

Yield stress, Fy

is the largest unit stress that the material achieves in a tension test.

Tensile stress, Fu

is the slope of the initial straight-line portion of the stress-strain diagram and is usually taken as 200,000 MPa for design calculation for all structural steel.

Modulus of Elasticity, E

is the ability of the material to undergo large inelastic deformations without fracture.

Ductility

is the ability of the material to absorb energy and is characterized by the area under a stress-strain curve

Toughness

is the ability of steel to be welded without changing its basic mechanical properties

.Weldability

is the ratio of the transverse strain to the longitudinal strain, is essentially the same for all structural steels, and has a value of 0 in the elastic rangeis the ratio of the shearing stress to shearing strain during the initial elastic behavior.

Poisson ratio

is the ratio of the shearing stress to shearing strain during the initial elastic behavior

Shear Modulus